The invention relates generally to the manufacture of electronic devices. More specifically, this invention relates to photoresist compositions and to photolithographic processes which allow for the formation of fine patterns using a negative tone development process.
Photoresists are photosensitive films used for the transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
Considerable effort has been made to extend the practical resolution capabilities of positive tone resist development, including in immersion lithography. One such example involves negative tone development (NTD) of a traditionally positive-type chemically amplified photoresist through use of particular developers, typically organic developers such as ketones, esters or ethers, leaving behind a pattern created by the insoluble exposed regions. See, for instance, U.S. Pat. No. 6,790,579.
Certain problems however can result with use of NTD processes. For instance, the relative UV intensity through a resist coating layer is decreased from upper to lower layer regions and from iso contant holes (C/Hs) to dense contact holes (C/Hs). In turn, the concentration of photo-generated acid also varies through a resist layer (acid will be present in decreased amounts in lower resist layer regions) and will vary from iso C/Hs to dense C/Hs. As a result, pattern profiles will exhibit undesirable T-top shapes, pattern collapse and missing contact holes may occur, and iso-dense bias and depth of focus margins may be at unacceptable levels.
Certain basic additives have been employed to attempt to improve resist resolution. See JPH11337722A; US2007190451; EP1702962B1; US20060172149;US20130177853; US20130344436; and US20140038102.
Electronic device manufacturers continually seek increased resolution of a patterned photoresist image. It would be desirable to have new photoresist compositions that could provide enhanced imaging capabilities.